1. Field of the Invention
The present invention relates to a process for manufacturing an amide compound. More particularly, the present invention relates to converting acrylonitrile to acrylamide by hydrating acrylonitrile in the presence of a metallic copper catalyst and a promoter therefor.
2. Description of the Prior Art
Known processes for the conversion of a nitrile, e.g. acrylonitrile and the like, to the corresponding amide, e.g. acrylamide and the like, by hydrating the nitrile in the presence of a metallic copper catalyst include, for example, those disclosed in U.S. Pat. No. 3,631,104 and Belgian Pat. No. 753,365, the latter corresponding to copending U.S. application Ser. No. 56,967, filed July 21, 1970, now U.S. Pat. No. 4,056,565. The catalysts employed in these processes are metallic copper catalysts having a comparatively large surface area such as reduced copper, Raney copper, Ullmann copper, etc., obtainable by the application of the respective reducing processes specifically developed therefor. In spite of the effectiveness of such metallic copper catalysts in converting nitriles to the corresponding amides, it has been desired to improve the catalytic effects thereof when using them on an industrial scale.
One process proposed for improving the conversion rate of nitrile to amide when using a metallic copper catalyst comprises adding a cupric salt of an inorganic acid, e.g. copper nitrate, or the cupric salt of a fatty acid, e.g. copper acetate, to the reaction mixture as a promoter for the metallic copper catalyst. This process is described in U.S. Pat. Nos. 3,911,009 and 3,962,333. It is shown therein that the conversion rate to the amide is increased by as much as 70% when using the metallic copper catalyst in conjunction with the cupric salt promoter, whereas the increase in the conversion rate when using a metallic copper catalyst alone without the promoter is only 50%. However, it is still desirable when operating on a commercial scale that a promoter be found which will increase the rate of conversion from nitrile to amide and also maintain the catalytic life of the metallic copper catalyst for longer periods of time.
In U.S. Pat. No. 3,869,511 certain anions are disclosed as promoters for solid catalysts which contain elemental copper in the catalytic hydration of acrylonitrile with water to acrylamide. Chloride is the anion most preferred by the patentees. However, bromide, nitrate, and nitrite are also disclosed as significantly improving the activity of the copper catalysts. The effective anion is introduced into the reaction solution as a water soluble salt of the effective anion. The patentees state that the cations of the salts appear to be inert with respect to any improvement of catalyst activity and almost any soluble salt of the selected anion can be selected. The alkali metal and alkaline earth metal salts are said to be suitable and the sodium salts are preferred for their economy.
In the prior art processes, the type of reactor employed depends on the shape of the metallic copper catalyst. For example, if the catalyst is metallic copper which is obtained by reducing copper oxide with hydrogen, a fixed bed reactor which is filled up with the tablet-shaped catalyst may be employed. If the catalyst is metallic copper which is obtained by: (a) dissolving out a part of a Raney alloy or, (b) reduction-crystallization from an aqueous solution of copper salt, a fluidized bed reactor may be employed, in which the catalyst used is suspended in a liquid medium.
In the aforesaid reaction systems, upon separation of the catalyst particles from the reaction product-containing solution, the pulverized catalyst which fills up a reactor and the fine particles in a suspension often pose a problem in handling. Namely, in the aforesaid catalyst systems composed of a metallic copper catalyst and a catalyst promoter problems arise during the separation of the metallic copper catalyst from the reaction solution. When separating by sedimentation, low settling rates are obtained. When separating by filtration, high pressure drops across the filter result.